Macrophage

Immune cells play surprising role in steady heartbeat

macrophages and heart cells
IT’S ELECTRIFYING Macrophages (green) “plug in” to heart cells (light purple and pink), providing an electrical boost that helps the heart cells contract and pump blood, a study in mice finds.

Immune system cells may help your heart keep the beat. These cells, called macrophages, usually protect the body from invading pathogens. But a new study published April 20 in Cell shows that in mice, the immune cells help electricity flow between muscle cells to keep the organ pumping.

Macrophages squeeze in between heart muscle cells, called cardiomyocytes. These muscle cells rhythmically contract in response to electrical signals, pumping blood through the heart. By “plugging in” to the cardiomyocytes, macrophages help the heart cells receive the signals and stay on beat.

Researchers have known for a couple of years that macrophages live in healthy heart tissue. But their specific functions “were still very much a mystery,” says Edward Thorp, an immunologist at Northwestern University’s Feinberg School of Medicine in Chicago. He calls the study’s conclusion that macrophages electrically couple with cardiomyocytes “paradigm shifting.” It highlights “the functional diversity and physiologic importance of macrophages, beyond their role in host defense,” Thorp says.

Matthias Nahrendorf, a cell biologist at Harvard Medical School, stumbled onto this electrifying find by accident.

Curious about how macrophages impact the heart, he tried to perform a cardiac MRI on a mouse genetically engineered to not have the immune cells. But the rodent’s heartbeat was too slow and irregular to…